GregF refers explicitly to what I had originally implied in my first post above. Trouble is, there are laws about discharging firearms, especially in urban environments; in Australia it is specifically prohibited.

So it's not my place to say that, when your backyard is unoccupied by a known companion animal and is thus routinely invaded by feral cats, but is surrounded by solid timber and there's no possibility of ricochet, the sound of a .22 short is unnoticed against the background urban hum of traffic. Two, though, pricks people's ears up and three will have them say "Some b--tard's shooting!"

These days I don't recommend what was once a very effective response; I've become gentler. And I live in the bush. Because I have the occasional Antechinus invading the kitchen I use Elliot traps (collapsible sheet aluminium traps that keep captives alive and restful for later release) and I use a larger version if I see any dumped cats. Dumped cats usually have a low survival rate but 4th generation ones can be huge; 12 kg (~28lb for you unmetricated ones) is the largest I've yet seen and it needed a feral pig trap to catch it.

A similar trap for the Burmese interloper (as used by people who relocate possums, raccoons etc) might be just the trick for Roz, who would then have a choice about any (or no) aversion therapy for the cat and its owner. Again, in Australia the Council Pound is a common destination for 'uncontrolled' domestic animals. Many councils have a requirement that domestic animals are microchipped, enabling the staff to locate the animal's owner who, on payment of a release fee, can take the animal home. If the animal has no microchip, tracing putative owners becomes more difficult but I'm sure community-minded people could offer suitable advice, after a week or so and before the pound's euthanasia policy is implemented

Cheers, Rowan